Gerald J. Wasserburg, John D. MacArthur Professor of Geology and Geophysics, Emeritus, passed away on June 13, 2016. He was 89 years old.
Wasserburg’s work established a time scale for the development of the early solar system including the end of the process of nucleosynthesis—the process by which atoms heavier than hydrogen formed—and the formation about 4.5 billion years ago of solid objects such as the earth and the moon, other planets, and certain meteorites. He also is acknowledged widely for his isotope studies of lunar materials collected by the Apollo missions and his involvement in U.S. space research programs. He and his colleagues also did important work on the dating of rocks, on the evolution of the earth through time, and on the modern oceans.
Wasserburg was born in New Brunswick, New Jersey, on March 25, 1927. He served in the U.S. Army from 1943 to 1946, then graduated from high school. He enrolled at Rutgers University under the GI bill, and later transferred to the University of Chicago, from which he earned his SB (1951), SM (1952), and PhD (1954) degrees.
Wasserburg joined Caltech faculty in 1955 as an assistant professor of geology. He became an associate professor in 1959, professor of geology and geophysics in 1963, MacArthur Professor in 1982, and he retired in 2001. He served as chair of the Division of Geological and Planetary Sciences from 1987 to 1989 and as executive officer for geochemistry over the same time period.
Not long after his arrival at Caltech, Wasserburg began the work that he is most famous for: leading the construction of the Lunatic I, a mass spectrometer for making high-precision measurements of lunar samples obtained by the Apollo missions.
The Lunatic I—now held in the collections of the National Museum of American History—”revolutionized the field of geochemistry,” says Donald Burnett, professor of nuclear geochemistry, emeritus, and one of Wasserburg’s longtime colleagues. “It totally changed the world because the precision with which you measure ratios of isotopes was an order of magnitude greater than before.”
Radioactive isotopes decay at a known rate into other isotopes. For example, about 10 percent of potassium-40 decays produce argon-40, with a half-life of 1.25 billion years. That means that one-half of the atoms of potassium-40 in a given sample—within a rock specimen recovered from the moon, for example—will decay over a 1.25 billion-year time span and about 10 percent of those decays yield argon-40; over the next 1.25 billion years, half of the remaining potassium-40 atoms will decay, and so on. Such rates of decay, which vary from isotope to isotope, provide a “clock” that can be used to determine the age of the specimen, provided you have an accurate accounting of the isotopes in your sample.
The Lunatic I was built at Caltech’s Central Engineering Services and installed in a new lab on the second floor of the Arms Laboratory at Caltech that Wasserburg named the “Lunatic Asylum.” Mass spectrometers separate ionized atoms according to their mass, and the Lunatic I—developed by Wasserburg and his then-graduate student Dimitri Papanastassiou (BS ’65, PhD ’70), now a faculty associate in geochemistry—was the first such instrument that was fully digital, with computer-controlled magnetic field scanning and rapid switching and digital ion beam measurement, enabling it to measure reliably isotope ratios with a precision that was a factor of 30 better than earlier instruments. “Those were exciting times,” Papanastassiou says. “We were doing things that nobody else could do.”
Wasserburg was invited in 1967 to be part of the team of scientists that would handle the initial processing of all of the lunar rocks collected by the Apollo astronauts. Together with Bob Walker of Washington University, Jim Arnold of the University of California at San Diego, and Paul Gast of Columbia University, he was one of the “Four Horsemen”—senior scientists who advised NASA during the Apollo missions.
The “inmates” of the Asylum (as Wasserburg referred to them) were among several teams of researchers to receive lunar rocks from the Apollo 11 mission, which, in July 1969, was the first to land humans on the moon. Each team had been tasked with independently studying the rocks—including to determine their age—with the results to be presented at the first Lunar Science Conference, held in Houston in January 1970.
At the conference, Wasserburg and his colleagues announced that the samples they had analyzed with Lunatic I were between 3.5 and 3.7 billion years old, with a high degree of accuracy. “Afterward, you saw everyone running around trying to quickly revise their talks,” Burnett recalls. “They had numbers for the age of the rocks too, but their margins of error were too big to be meaningful.”
Wasserburg continued research on lunar samples through the end of the Apollo program. The crew of the Apollo 13 mission—which was forced to abort its lunar landing because of an onboard explosion—gave Wasserburg a photo bearing the inscription, “Sorry we couldn’t bring back any rocks.” It remained on his wall for decades.
When President Richard Nixon moved to cancel the final two Apollo missions, 16 and 17, the Four Horsemen organized a protest from the scientific community. The missions were reinstated.
In later research, Wasserburg discovered the presence of the decay products of the short-lived radioactive isotope aluminum-26 in the oldest remnants of the solar system, suggesting that a nearby supernova contributed matter to the solar nebula shortly before it collapsed and accreted to form the sun and planets. Lunatic 1 also played a key role in discovering the first evidence of the “late heavy bombardment”, a period, roughly 4 billion years ago, when the moon was pummeled by asteroids and comets. Ultimately, his advances in dating techniques contributed to the timeline for the evolution of the solar system that we know today.
Colleagues remember Wasserburg as a driven and competitive scientist who was always excited about his work. “Every day, he really believed that the work he’d done in the lab yesterday was the best science of the past 10 years,” Burnett says. Wasserburg’s painstaking attention to detail was well known. “He had very high standards for himself and everyone else, and was strongly supportive of young scientists at the Institute” says Geoffrey Blake (PhD ’86), professor of cosmochemistry and planetary sciences and professor of chemistry. “Those are the kind of people who make Caltech special.”
Wasserburg was the recipient of the Crafoord Prize in Geosciences in 1986 and numerous other honors, including the Arthur L. Day Medal from the Geological Society of America (1970), the NASA Distinguished Public Service Medal (1972 and 1978), the Wollaston Medial of the Geological Society of London (1985), the Gold Medal of the Royal Astronomical Society (1991), and the William Bowie Medal of the American Geophysical Union (2008). He was a member of the National Academy of Sciences, the American Philosophical Society, the American Academy of Arts and Science, and the Norwegian Academy of Science and Letters.
He is survived by Naomi Wasserburg, his wife of more than 60 years, and his sons Charles and Daniel Wasserburg.
Gerald J. Wasserburg, John D. MacArthur Professor of Geology and Geophysics, Emeritus, passed away on June 13, 2016. He was 89 years old.
Gerry Wasserburg’s research focused on the origins and history of the solar system and its component bodies. His work established a time scale for the development of the early solar system including the end of the process of nucleosynthesis and the formation about 4.5 billion years ago of solid objects such as the earth and the moon, other planets, and certain meteorites. He also is acknowledged widely for his isotope studies of lunar materials collected by the Apollo missions and his involvement in U.S. space research programs. He and his colleagues also did important work on the dating of rocks, on the evolution of the earth through time, and on the modern oceans.
Wasserburg earned his SB, SM, and PhD degrees from the University of Chicago (in 1951, 1952, and 1954), and joined the Caltech faculty in 1955 as an assistant professor of geology. He became an associate professor in 1959, professor of geology and geophysics in 1963, MacArthur Professor in 1982, and he retired in 2001.
He served as chair of the Division of Geological and Planetary Sciences from 1987 to 1989 and as executive officer for geochemistry over the same time period.
He was the recipient of numerous honors, including the Arthur L. Day Medal from the Geological Society of America (1970), the NASA Distinguished Public Service Medal (1972 and 1978), the Wollaston Medial of the Geological Society of London (1985), the Crafoord Prize in Geosciences (1986), the Gold Medal of the Royal Astronomical Society (1991), and the William Bowie Medal of the American Geophysical Union (2008). He was a member of the National Academy of Science, the American Philosophical Society, the American Academy of Arts and Science, and the Norwegian Academy of Science and Letters.
A full obituary will be published at a later date.
Chiral molecules—compounds that come in otherwise identical mirror image variations, like a pair of human hands—are crucial to life as we know it. Living things are selective about which “handedness” of a molecule they use or produce. For example, all living things exclusively use the right-handed form of the sugar ribose (the backbone of DNA), and grapes exclusively synthesize the left-handed form of the molecule tartaric acid. While homochirality—the use of only one handedness of any given molecule—is evolutionarily advantageous, it is unknown how life chose the molecular handedness seen across the biosphere.
Now, Caltech researchers have detected, for the first time, a chiral molecule outside of our solar system, bringing them one step closer to understanding one of the most puzzling mysteries of the early origins of life.
A paper about the work appears in the June 17 issue of the journal Science.
The different forms, or enantiomers, of a chiral molecule have the same physical properties, such as the temperatures at which they boil and melt. Chemical interactions with other chiral species, however, can vary greatly between enantiomers. For instance, many chiral pharmaceutical chemicals are only effective in one handedness; in the other, they can be toxic.
“Homochirality is one of the most interesting properties of life as we know it,” says Geoffrey Blake (PhD ’86), professor of cosmochemistry and planetary sciences and professor of chemistry. “How did it come to be that all living things use one enantiomer of a particular amino acid, for example, over another? If we could run the tape of life again, would the same enantiomers be selected through a deterministic process, or is a random choice made that depends on a tiny imbalance of one handedness over the other? If there is life elsewhere in the universe, based on the biochemistry we know, will it use the same enantiomers?”
To help answer these questions, Blake and his colleagues at the National Radio Astronomy Observatory (NRAO) searched one particular molecular cloud, called Sagittarius B2(N), for chiral molecules. The team used the Green Bank Telescope Prebiotic Interstellar Molecular Survey (PRIMOS) of Sagittarius B2(N). The PRIMOS project, led by co-senior author Anthony Remijan of the NRAO, examines the spectrum of Sagittarius B2(N) across a broad range of radio frequencies. Every gas-phase molecule can only tumble in specific ways depending on its size and shape, giving it a unique rotational spectrum —like a fingerprint—that makes it readily identifiable in the PRIMOS survey.
The PRIMOS data revealed the signature of a chiral molecule called propylene oxide (CH3CHOCH2); follow-up studies with the Parkes radio telescope in Australia confirmed the findings. “It’s the first molecule detected in space that has the property of chirality, making it a pioneering leap forward in our understanding of how prebiotic molecules are made in space and the effects they may have on the origins of life,” says Brandon Carroll, co-first author on the paper and a graduate student in Blake’s group. “While the technique we used does not tell us about the abundance of each enantiomer, we expect this work to enable future observations that will let us understand a great deal more about chiral molecules, the origins of homochirality, and the origins of life in general.”
Propylene oxide is a useful molecule to study because it is relatively small compared to biomolecules such as amino acids; larger molecules are more difficult to detect with radio astronomy, but have been seen in meteorites and comets formed at the birth of the solar system. Though propylene oxide is not utilized in living organisms, its presence in space is a signpost for the existence of other chiral molecules.
“The next step is to detect an excess of one enantiomer over the other,” says Brett McGuire (PhD ’15), an NRAO Jansky Fellow and former member of the Blake lab, who shares first authorship on the work with Carroll. “By discovering a chiral molecule in space, we finally have a way to study where and how these molecules form before they find their way into meteorites and comets, and to understand the role they play in the origins of homochirality and life.”
“The past few years of exoplanetary science have told us there are millions of solar system-like environments in our galaxy alone, and thousands of nearby young stars around which planets are being born,” says Blake. “The detection of propylene oxide, and the future projects it enables, lets us begin to ask the question—does interstellar prebiotic chemistry plant the primordial cosmic seeds that determine the handedness of life?”
Additional coauthors on the paper, titled “Discovery of the interstellar chiral molecule propylene oxide (CH3CHOCH2),” include Caltech graduate student Ian Finneran, a member of the Blake group. The work is supported by the National Science Foundation Astronomy and Astrophysics and Graduate Fellowship grant programs and the NASA Astrobiology Institute through the Goddard Team and the Early Career Collaboration award program.
Naturally formed quasicrystals—crystal-like solids with supposedly impossible symmetries—are among the rarest structures on Earth. Only two have ever been found.
A team led by Paul Asimow (MS ’93, PhD ’97), professor of geology and geochemistry at Caltech, may have uncovered one of the reasons for that scarcity, demonstrating in laboratory experiments that quasicrystals could arise from collisions between rocky bodies in the asteroid belt with unusual chemical compositions.
A paper on their findings was published on June 13 in the advance online edition of the Proceedings of the National Academy of Sciences.
At an atomic level, crystals are both ordered and periodic, meaning that they have a defined geometric structure, with that structure repeating itself over and over. To grow such a repeating structure without the original organization breaking down, the crystal can only exhibit one of four types of rotational symmetry: two-fold, three-fold, four-fold, or six-fold.
The number refers to how many times an object will look exactly the same within a full 360-degree rotation about an axis. For example, an object with two-fold symmetry appears the same twice, or every 180 degrees; an object with three-fold symmetry appears the same three times, or every 120 degrees; and an object with four-fold symmetry appears the same four times, or every 90 degrees.
Prior to 1984, it was believed that it would be impossible for a crystal to grow with any other type of symmetry; no examples of crystals with other symmetries had been discovered in nature or grown in a lab. In that year, however, Princeton physicist Paul Steinhardt (BS ’74) theorized a set of conditions under which other types of symmetry could potentially exist and Dan Shechtman of the Israel Institute of Technology published a paper announcing the creation of a crystal-like structure with a five-fold rotational symmetry.
These structures were ordered enough to produce recognizable diffraction patterns when shot with high-energy beams of electrons and X-rays—unlike disordered structures, which produce no patterns. However, the crystal-like structures were not periodic—that is, their organization shifted and changed as they grew. The materials were dubbed “quasiperiodic crystals,” or “quasicrystals” for short.
Over the next few decades, researchers figured out how to manufacture more than 100 different varieties of quasicrystals by melting and homogenizing certain elements and then cooling them at very specific rates in the lab. Still, though, no naturally existing quasicrystals were known. Indeed, researchers suspected their formation would be impossible. That is because most lab-grown quasicrystals were metastable, meaning that the same combination of elements could arrange themselves into a crystalline structure using less energy.
Everything changed in the late 2000s, when Steinhardt and colleague Luca Bindi from the Museum of Natural History at the University of Florence (currently in the Faculty of the Department of Earth Sciences of the same University) found a tiny grain of an aluminum, copper, and iron mineral that exhibited five-fold symmetry. The grain came from a small sample of the Khatyrka meteorite, an extraterrestrial object known only from a few pieces found in Russia’s Koryak Mountains. Steinhardt and his collaborators found a second natural quasicrystal from the same meteorite in 2015, confirming that the natural existence of quasicrystals was possible, just very rare.
A microscopic analysis of the meteorite indicated that it had undergone a major shock at some point in its lifetime before crashing to Earth – likely from a collision with another rocky body in space. Such collisions between are common in the asteroid belt and release high amounts of energy.
Asimow and colleagues hypothesized that the energy released by the shock could have caused the quasicrystal’s formation by triggering a rapid cycle of compression, heating, decompression, and cooling.
To test the hypothesis, Asimow simulated the collision between two asteroids in his lab. He took thin slices of minerals found in the Khatyrka meteorite and sandwiched them together in a sample case that resembles a steel hockey puck. He then screwed the “puck” to the muzzle of a four-meter-long, 20-mm-bore single-stage propellant gun, and blasted it with a projectile at nearly one kilometer per second, about equal to the speed of the fastest rifle-fired bullets.
It is important to note that those minerals included a sample of a metallic copper-aluminum alloy, which has only been found in nature in the Khatyrka meteorite.
After the sample was shocked with the propellant gun, it was sawed open, polished, and examined. The impact smashed the sandwiched elements together and, in several spots, created microscopic quasicrystals.
Armed with this experimental evidence, Asimow says he is confident that shocks are the source of naturally formed quasicrystals. “We know that the Khatyrka meteorite was shocked. And now we know that when you shock the starting materials that were available in that meteorite, you get a quasicrystal.”
Sarah Stewart (PhD ’02)—a planetary collision expert from the University of California, Davis, and reviewer of the PNAS paper—admits she was surprised by the findings. “If you had called me before the study and asked if this would work I would have said ‘no way.’ The astounding thing is that they did it so easily,” she says. “Nature is crazy.”
Asimow acknowledges that the experiments leave many questions unanswered. For example, it is unclear at what point the quasicrystal formed during the shock’s pressure and temperature cycle. A bigger mystery, Asimow says, is the origin of the copper-aluminum alloy in the meteorite, which has never been seen elsewhere in nature.
Next, Asimow plans to shock various combinations of minerals to see what key ingredients are necessary for natural quasicrystal formation.
These results are published in a paper titled “Shock synthesis of quasicrystals with implications for their origin in asteroid collisions.” In addition to Asimow, Steinhardt, and Bindi, other coauthors on the paper are Chi Ma, director of analytical facilities in the Geological and Planetary Sciences division at Caltech; Lincoln Hollister (PhD ’66) and Chaney Lin from Princeton University; and Oliver Tschauner from the University of Nevada, Las Vegas. Their work was supported by the National Science Foundation (NSF), the University of Florence, and the NSF-Materials Research Science & Engineering Centers Program through New York University and the Princeton Center for Complex Materials.
To get a glimpse into the future, what better place is there to look than the minds of those about to become Caltech’s newest alumni? After all, our 2016 graduates have been at the forefront of research in vastly different fields for the past few years. Their unique perspectives have informed their ideas of the future, and their work will reach far beyond the confines of a lab.
With that in mind, in the Summer 2016 issue of E&S magazine, we talked to a handful of undergraduate and graduate students prior to commencement to find out what they think will be the next big thing in science and engineering and how their plans after graduation reflect those ideas.
I believe that the future of science, technology, engineering, and mathematics (STEM) will place a greater emphasis on implementation and impact of research. While rapid economic growth and globalization have introduced numerous difficult challenges, society has acquired powerful new tools and technology to develop and implement solutions for these issues.
I will be working as a management consultant after graduating to expose myself to business and strategy. That way, I can perhaps one day help new discoveries and ideas produce a tangible impact on people’s lives.”
BS in Computer Science
I believe the future of planetary and space exploration will follow two paths—one, the search for life beyond Earth within the solar system, and two, the characterization of exoplanets.
For the solar system, the initial survey of its major worlds was just completed with the New Horizons flyby of Pluto, and therefore a new focus will likely emerge. That initial survey has revealed several worlds to be potentially habitable, including Mars, Europa, and Enceladus, with the former two already targets for future missions. These new missions will not only reveal more about these worlds but also force us to reevaluate what life is, how it arises, and how it endures.
For exoplanets, the diversity of worlds is immense. From giant planets that orbit their host stars in less than a day to habitable planets with permanent daysides and nightsides, exoplanets offer a tremendous opportunity to understand the planets in our own solar system. With the rapid development of technologies, instruments, and observing techniques, the flood of data regarding exoplanets will only continue. I plan to be among the scientists who will analyze this data and combine their results with theoretical models to investigate what these distant worlds are like. By doing this, we will be exploring our place in the universe and whether we are alone within it.”
PhD in Planetary Science
When asked what he would do with his degree in philosophy during a routine dentist appointment, David Silbersweig, MD at Brigham and Women’s Hospital and Academic Dean at Harvard Medical School, responded with a single word that spoke volumes: ‘Think.’ Simply put, I too want to think.
I want to learn how to think at a complex level such that my ability to think and subsequently solve problems allows me to change lives. The history and philosophy of science degree at Caltech has given me exactly this. According to Silbersweig, ‘If you can get through a one-sentence paragraph of Kant, holding all of its ideas and clauses in juxtaposition in your mind, you can think through most anything.’ In my first History and Philosophy of Science class, I read Kant. I also find immense happiness in working with and helping other individuals, a sense of euphoria matched by little else in life. I learned this lesson through tutoring students and coaching younger athletes. And finally, as a collegiate athlete myself, I have undergone multiple orthopedic surgeries that ignited an interest in the musculoskeletal system and its ability to suffer injury yet recover remarkably. Together, these three aspects of life are central to my vision of the future. Becoming an orthopedic surgeon is the perfect combination—the career that will give me these components and a lot more.
One of the major developments in medicine will be 3-D printing, primarily in order to provide individuals with replacement bones and organs. Combining new progress in computer science will facilitate immense progress in 3-D printing, which also aligns well with the use of robotics in surgery. As an athlete who has torn my ACL and had bone spurs in the past year, I’m excited to be a part of this field in the future and hopefully help other athletes succeed in pursuing their passions.”
BS in History and Philosophy of Science
My personal hunch, and perhaps a somewhat common one, is that all disciplines—and not just STEM ones—are moving toward being increasingly data driven, a phenomenon rooted in freer dissemination and greater influx of research data. Correspondingly, computers and programming drive data processing in all disciplines; a common joke is that every scientist is automatically a software engineer. Statistical and machine learning techniques that are designed to tackle vast quantities of data are increasingly common in academic papers and will probably continue to climb in popularity.
I am planning to go into computational astrophysics research because I believe that the recent influx of data from new detectors will drive a huge surge of research questions to be investigated. And as a physics/computerscience double major, I’m uniquely equipped to analyze big data and extract scientific meaning from it.”
BS in Physics and Computer Science
Many aspects about future climate are unclear, such as how cloudiness, precipitation, and extreme events will change under global warming. But recent progress in observational and computational technology has provided great potential for clarifying these uncertainties. I plan to continue my research and utilize new data and models to develop theoretical understanding of these problems. I hope that such new insight will be helpful for assessing climate change impacts and designing effective adaptation and mitigation strategies.”
PhD in Environmental Science and Engineering
The future of science and engineering depends on closing the huge gap between the general public and scientists and engineers. I think this stems from a good deal of ignorance about what it is we do and hope to achieve, which leads to misconceptions about our work and community, and the separation between ‘us’ and ‘them.’ But if we’re trying to understand and solve problems that affect everyone, shouldn’t everyone be more involved?
When I graduate, I’m going to take a year off to try and bridge this gap in my own life. I don’t know what I’ll do yet, but it will be decidedly nonacademic. I want to travel, work odd jobs, and pursue hobbies I’ve set aside to finish my education. If I want to help people understand why I do what I do, I need to be certain that I understand first. After only four years surrounded almost exclusively by scientists and engineers, I want to get away a little. That way, when I inevitably return, I’ll have a bit more perspective.”
BS in Mechanical Engineering and Planetary Science
Driven by the goal of reducing fossil fuel use and pollution, clean energy research plays and will play a pivotal role in America’s energy future. Clean energy research spans disciplines such as biological and environmental sciences, advanced materials, nuclear sciences, and chemistry. Therefore, multidisciplinary efforts are not only necessary but also crucial to develop and deploy real-world solutions for energy security and protecting the environment.
As a graduate student, I have focused on understanding nanoscale energy transport in novel energy-efficient materials. In the future, I plan to further advance and apply my expertise to solve real-world problems in an integrated and multidisciplinary approach. I hope this effort will eventually lead to developing advanced clean energy technologies that could not only ease today’s energy crisis but also improve our quality of life.”
PhD in Mechanical Engineering
I believe that in the next decade, the behavioral and computational subfields of neuroscience will work together seamlessly. I think this change will be primarily fueled by the development of new tools that allow us to measure the activity of large populations of neurons more precisely.
A prominent behavioral method of research, in mice at least, is to activate large structures in the brain and observe the aggregate behavioral effect. However, it is unlikely that all of these neurons are responsible for the same signal, so this approach may be too crude. I think new measurement techniques will enable behavioralists to collect large-scale population activity that computationalists can use in order to find subtle differences of function within these structures. Hopefully this collaboration will lead to generating and validating fundamental theories underlying how the brain works.
Currently, I am in the process of developing a method to measure the activity from over 10,000 neurons simultaneously. I hope to validate this technique before I graduate and then apply it to studying large-scale population activity during various behaviors. My future aim is to work closely with computationalists with the hope of discovering fundamental theories of brain function.”
BS in Biology
I think the future of planetary science is to discover and characterize more and more extra-solar planets, including their orbital configurations, atmospheres, and habitability. This is a challenging task because it requires a solid understanding of how chemistry and physics work on a planetary scale. Learning more about the planets closest to us paves a way toward the understanding of exoplanets that are far beyond our reach, since we can send missions to them. So after graduation, I will join the team for Juno—the spacecraft that will arrive at Jupiter in summer 2016—at JPL. New discoveries about Jupiter will also tell us more about what other planets beyond our solar system could look like.”
PhD in Planetary Science
The global ecological system is collapsing and dying as humanity overruns natural ecosystems and the climate. We are entering an age of unrelenting violence and suffering, prior to biosphere collapse and the end of being, unless dramatic social change based upon a global ecology ethic arises quickly. Humans evolved within... EcoInternetRead More